By Howard E. Strassler, DMD

Interim restorations are a critical component of fixed prosthodontic treatment, biologically and biomechanically.1 These restorations are also referred to as provisional restorations or temporary restorations. When treatment planning to restore a tooth with a full-coverage crown restoration, there are sequential steps that must be followed to ensure an easy, predictable final result—the successful try-in and cementation of the final crown. The same is true for multiple restorations in the same quadrant or for fixed partial dentures (FPD). Independent of the restorative material, the final crown or FPD is fabricated from all-ceramic, porcelain-metal, or all-metal, and the placement of the definitive restoration requires that the restoration have physiologic proximal and occlusal contact. Achieving this result and ensuring minimal adjustment of the laboratory-fabricated restoration during insertion requires that a well-made, smooth, well-adapted, well-fitting, and well-adjusted provisional restoration be placed and reused between appointments until the definitive restoration is cemented.

Temporary or provisional single-crown or FPD restorations protect the underlying tooth preparation and the pulp while the definitive restoration is being fabricated by the laboratory. This pulpal protection promotes pulpal healing after the trauma of tooth preparation. Also, a well- adapted and contoured provisional crown ensures the return to health of any traumatized soft tissues during the crown preparation and impression making by allowing the patient to maintain their oral hygiene adjacent to the temporary crown with brushing and flossing.2 Polishability, plaque retentiveness, and techniques for coating and smoothing the surface all can affect periodontal health. To allow for the maintenance of periodontal health, the materials used for provisional restorations need to smooth, and not be plaque- retentive.3-5

Temporary restorations also provide the clinician with critical information by helping the clinician to decide whether or not there is adequate occlusal clearance and reduction of the tooth preparation for the final restoration.2 In the case of anterior esthetic restorations, the provisional crowns can provide the clinician with guidance as an esthetic trial to the color, contour, length, width, and shape of the teeth before fabrication of the final porcelain-metal or all-porcelain restoration.6 If more than one tooth is being restored, provisional crowns provide important diagnostic information that help to determine the desired occlusal relationships, and in cases where the crowns are being used to alter the occlusal vertical dimension, these provisional restorations are a guide to the desired occlusal position. The materials used for provisional restorations must be durable enough to stay in place during the duration of time required for the steps required and the return and placement of the definitive restoration.

Provisional restorations must be easy to remove without damaging the existing tooth preparation. Other important purposes for the provisional restoration include the maintenance of the tooth preparation position both occlusally and proximally.7-10 The provisional restoration should be adjusted to duplicate the desired final occlusion and must have proximal contact with adjacent teeth to avoid tooth movement and shifting that can have a negative impact on the placement of the final restoration. If the tooth or teeth that have been prepared shift after the impression is made, the restoration(s) created by the laboratory will very likely require additional chair time for making what will be necessary adjustments of the proximal contacts and occlusal adjustment during the try-in before cementation. In some cases, the movement of the tooth preparation can change the path of insertion for the final crown or FPD and may not allow complete seating of the restoration during try-in. For a multiple-unit FPD with a metal framework, that restoration may need to be sectioned for soldering, and if the FPD is all-ceramic, it may require a new impression and refabrication of the restoration. In extreme cases when teeth have moved as a result of the loss or fracture of the provisional restoration, the clinician might have to fabricate acrylic resin copings and make a pick-up impression so that the laboratory has the new tooth preparation positions when it is prefabricating the final restoration.11,12 In some cases, as a result of tooth movement, the preparation might need to be orthodontically repositioned or the teeth re-prepared. This leads to a significant increase in chair time and may lead to patient dissatisfaction because of the additional procedures and office visits. For the tooth that has shifted only a minor amount, the consequences may only be an increase in chair time during the cementation appointment.

The fabrication of temporary restorations for a single crown requires proficiency with a variety of materials and techniques that can be used to make well- adapted and functional provisionals. There are many choices to temporize a single crown. These choices include prefabricated metal crowns, polycarbonate crowns, celluloid crowns, composite resin crowns, acrylic resin for custom provisionals, bis- acryl or bis-GMA automix composite resin materials, and composite resin for custom fabrication.2,8-10,13,14 For multi-unit FPDs, the clinician has the choice of acrylic resins, bis-acryl or bis-GMA automix composite materials, or laboratory-fabricated resin shells. Part 1 of this article will review polymeric resin provisional materials; Part 2 will review single-unit, preformed crowns.

The most commonly used provisional restorative materials are polymeric resins. Polymeric resins can be divided intotwo subclasses:acrylic resin and composite resin(Table 1). The same techniques have been describedwhen using both types of polymeric resins tofabricate provisional restorations duringprosthodontic treatment.

Acrylic resin provisional materials typically refer totwo different chemical materials: polymethylmethacrylate(PMMA) and polyethylmethacrylate (PEMA). Thereare other dentalresins, but for this article the author willrefer to the two most commonly usedacrylic resins. These resins are also referredto as self-curing, autopolymerizing, and cold-cure.13 One very well-accepted material that has been and continues to be used for the fabrication of temporary restorations is acrylic resin. Typically, when fabricating a temporary restoration with acrylic resin, a custom shell that will be relined with acrylic resin at the time of tooth preparation, and mimics the final contours and anatomy of the desired temporary restoration, can be used. Another technique is the use of a carrier matrix (template) for the provisional restorative material that has been fabricated before the tooth-preparation appointment. The dental literature describes the use of warmed wax, premade acrylic shells, vacuum-formed polypropylene matrices, and vinyl polysiloxane impressions for this carrier matrix.8-10,15-17 When evaluating matrix types on the surface roughness of resin, there was no universal matrix that produces the smoothest surface for the resin.18

With acrylic resin, the fabrication of the provisional restoration usually requires mixing a powder and liquid together to form a paste that is placed in a premade shell, a template, or a carrier that is placed over the tooth preparation. When the acrylic resin reaches a rubbery consistency, the carrier is removed with the acrylic resin from the tooth preparation so that the resin can achieve complete polymerization and hardening. It is usually difficult to time the setting and working stages of the polymerization reaction of acrylics because of the inaccurate method that the polymer powder and liquid monomer are dispensed. Although these materials are tooth-colored and relatively inexpensive, they are difficult to manipulate and have poor physical properties.9,19 Powder-liquid acrylic resins are typically PMMA but they can be PEMA. When using resins, the clinician should know which resin is being used. These materials can be difficult to use because they are mixed as powder to liquid. The consistency from runny liquid to putty occurs over several minutes. Other difficulties with acrylic resins are their relatively high polymerization shrinkage and the generation of significant heat during polymerization. Care must be taken to avoid pulpal and gingival damage to remove the acrylic resin before excessive heat of polymerization occurs.10,13 As described earlier, when using these materials to minimize resin shrinkage, the provisional crown or FPD should be placed in a cup of room-temperature water while in a rubbery state. Although hot water will accelerate the set of the resin, the hot water and heat polymerization will cause the resin to shrink and distort at a greater rate than if the resin is setting in room-temperature water.20 Room-temperature water will equalize the heat of polymerization of the acrylic resin.7,10,20 Also, on rare occasions, acrylic resins can cause allergic hypersensitivity.21-23 When using acrylic resins there is an unpleasant odor while setting.9,19,20,24 These resins also have a high coefficient of thermal expansion, low strength, low modulus of elasticity, and poor abrasion resistance to wear.19,20 For the time period that these resins will be used, they are dimensionally stable and stain resistant.6,25,26

Evidence has shown that the more complex the case, especially multi-unit, multi-pontic clinical situations with the requirement of long-term durability, having the ability to reline marginal areas and repair fractures with acrylic resin is critical, and PMMA provisional materials are generally the materials of choice.9,27,28 Also, for long-span FPDs fabricated with acrylic resins, an increase in flexural strength and resistance to breakage can be attained through the use of fiber reinforcement embedded in the provisional material.29,30

In recent years, composite resin provisional materials have been introduced. These materials were developed to overcome some of the deficiencies of acrylic resin for interim crownrestorations. These materials have improved physical properties and provide for more predictable and easier fabrication of aprovisional crown restoration.15,16,19,20,24,31-33 The chemistry of these provisional composite resins are either bis-acryl or bis-GMA resins. They are typically dispensed in a double-barrel tube configuration where the catalyst and base pastes are mixed in automixing tips, and they are used in a similar manner to acrylic resins. The provisional composite resin material is placed in a matrix carrier, placed over the tooth preparations, removed, and then trimmed, adjusted, and polished (Figure 1A, Figure 1B, Figure 1C, Figure 1D and Figure 2A, Figure 2B, Figure 2C). The majority of auto-mix provisional composite resins are bis-acryl resins. Other provisional composite materials for single crowns are manufactured as a preformed composite crown (Protemp™, 3M ESPE, St. Paul, MN) (Figure 3), or as a composite resin putty stick (Revotek LC, GC America, Alsip, IL) where the desired amount of composite resin is cut from the putty stick for use in fabricating the provisional restoration. Typically, provisional composite materials have significantly less shrinkage than acrylic resin because of the presence of radiopaque glass fillers, which also improves the fit of the provisional restoration to the tooth preparation.16,33,34 Glass fillers also improve the wear characteristics of the material.

When a bis-acryl composite resin provisional material was compared to PMMA, one study concluded that a bis-acryl composite resin was significantly superior to PMMA as a provisional restorative material based on physical properties.34 One concern with resin-based restorative materials is environmental damage because of dietary solvents. Bis-acryl composites were more resistant to the problems of wear and color changes than other provisional materials.34,35

Bis-acryls have a paste-paste formulation which undergoes a three-stage polymerization reaction. The first phase goes from a free-flowing paste that adapts to the tooth preparation and then becomes elastic within 60 to 75 seconds. The second phase, over the next 4 minutes, is a cross-linking polymerization reaction allowing the polymer to reach a high compressive strength. The final phase of polymerization allows the resin to reach its final hardness within 5 minutes after initial mixing so that the restoration can be adjusted and polished before cementation.

It has been reported that bis-acryl composites used for provisional restorations have advantages over other resin-based provisional materials.2,7,15,16,20,29-31,34-38 These advantages include:

Because it is a filled composite resin, it is harder, more resistant to dietary solvents, and more resistant to occlusal wear than unfilled acrylic resin.

It is quick and easy to use; it sets rapidly so that it can be removed from the mouth after 60 to 75 seconds with less chance of causing thermal damage to the pulp.

It is flexible so insertion and removal is easier.

It has a lower modulus to withstand occlusal forces and breakage.

It has minimal polymerization shrinkage and minimal heat of polymerization.

It is radiopaque.

It can be easily repaired with a flowable composite resin.39,40

It has excellent color stability and stain resistance.

It has little odor when mixed.

Protemp Crown temporization material is a light-cured, composite resin,preformed crownfor single-unit crown temporization ofmandibular premolars and molars, maxillarypremolars and molars, and canines. It combinesthe advantages of composite-based temporization materials, such as fit, wear resistance, and esthetics, with the advantages of prefabricated crowns, such as fit, ease of use, no need for an additional matrix, and easyclean-up. It is a preformed, moldable composite-based crown that canbe fit and adapted in less than 4 minutes. Thisnovel temporizationmaterial has an improvement in physicalproperties when compared to other preformed provisional materials.14 In its uncured condition, it handles like putty that can be easily molded and reshaped using traditional composite instruments (Figure 4). Its moldable state offers the ease of adaptation to the buccal, lingual, and interproximal margins with the additional advantage of attaining proximal and occlusal contacts before light-curing. It can be polished similar to any composite resin or a paint-on liquid polish (Figure 5).

Provisional or interim restorations are an important element of fixedprosthodontic treatment both biologically andbiomechanically.1 These restorations provide an important diagnostic function while in place, as well as being critical in evaluating the physiologic position of the final restoration. In the esthetic zone, they are important in evaluating the esthetics for the definitive restoration. One can view the provisional restoration as a blueprint for the design of the definitive prosthesis.1 There are many choices of materials for use as interim restorations. It is important that the clinician make their selection based on the clinical needs for each patient. As part of these considerations, the clinician must understand how the physical properties, handling characteristics, patient response to the appearance of the interim restoration, durability of the restoration, and the material cost affect the final outcome. There is no doubt that no single material meets all of the requirements for provisional restorations. Also, the classification of any provisional restorative material does not ensure clinical success based on general physical properties. The selection of provisional materials should be made based on a case- by-case evaluation for any given patient. Based on the evidence, it appears that bis-acryl and bis-GMA materials are, in most cases, appropriate for single-unit restorations and less complex three- or four-unit FPDs. The more complex the case, especially multi-unit, multi-pontic clinical situations with the requirement of long-term durability, relining marginal areas and repairing fractures with the use of PMMA provisional materials are generally better-suited.41-43 There is no one perfect, ideal material. Perhaps of greatest importance isthe clinician’s mastery of techniques for handling and using multiple materials to achieve physiologic provisional restorations.